1. Field of the Invention
The present invention relates to a condenser microphone, and more particularly to a directional silicon condenser microphone having an additional back chamber.
2. Description of the Related Art
Generally, a condenser microphone widely used in a mobile communication terminal and an audio system comprises a voltage bias element, a pair of a diaphragm/backplate for constituting a capacitor C varying according to a sound pressure, and a JFET (Junction Field Effect Transistor) for buffering an output signal. The conventional the condenser microphone is assembled by sequentially inserting a vibrating plate, a spacer ring, an insulation ring, a backplate and a conductive ring in a case, and finally inserting a PCB and curling an end portion of the case toward the PCB.
Recently, a semiconductor processing technique using a micromachining is proposed as a technique for integrating a microscopic device. The technique, also known as a MEMS (Micro Electro Mechanical System) employs a semiconductor manufacturing process, an integrated circuit technology in particular, to manufacture a microscopic sensor, an actuator and an electromechanical structure having a size in a unit of μm. In accordance with a MEMS chip microphone manufactured via the micromachining technology, conventional components of the microphone such as the vibrating plate, the spacer ring, the insulation ring, the backplate and the conductive ring may be miniaturized and integrated, and may have a high performance, a multi-function, a high stability and a high reliability through a high precision microscopic process.
FIG. 1 is a diagram exemplifying a conventional MEMS chip structure used in a silicon condenser microphone. Referring to FIG. 1, a MEMS chip 10 has a structure wherein a backplate 13 is formed on a silicon wafer 14 using a MEMS technology and a vibrating plate 11 is disposed having a spacer 12 therebetween. The backplate 13 includes a sound hole 13a formed therein, and the MEMS chip 10 is generally manufactured by the micromachining technology and a semiconductor chip manufacturing technology.
FIG. 2 is a lateral cross-sectional view illustrating a conventional silicon condenser microphone employing the MEMS chip. Referring to FIG. 2, a conventional silicon condenser microphone 1 is assembled by mounting the MEMS chip 10 and a ASIC (application specific integrated circuit) chip 20 on a PCB 40 and inserting the same in a case 30 having a sound hole 30a formed therein.
However, as shown in FIG. 2, because a back chamber 15 of the conventional silicon condenser microphone 1 is formed by the MEMS chip 10, a space of the back chamber 15 is extremely small due to a size of the MEMS chip 10 which is a semiconductor chip. Therefore, a sound quality of the microphone is degraded.